SpriteBatch and slow simulation

Hello everyone,
I'm here with a very newbie question.
I've seen "HelloWorld" example, and this use an orthographic camera for the rendeing, this example works without any problems.
Then I've created a new project from scratch, and instead of an orthographic camera I used the simple SpriteBatch for the rendering. The project works, but very very slowly.
Here some of the project code:

Actually SpriteBatch uses an orthographic projection for rendering. Your problem is something else. You have to scale all units to MKS (meters kilos seconds) system. It is all over this discussion board, just search for MKS. Essentially that means your physics
objects need to be in meters and you need to somehow scale between pixels and meters for your drawing code. In source control there is a new HelloWorld XNA sample, which shows you how it is done using the spritebatch.

Actually SpriteBatch uses an orthographic projection for rendering. Your problem is something else. You have to scale all units to MKS (meters kilos seconds) system. It is all over this discussion board, just search for MKS. Essentially that means your physics
objects need to be in meters and you need to somehow scale between pixels and meters for your drawing code. In source control there is a new HelloWorld XNA sample, which shows you how it is done using the spritebatch.

A simple solution to the slow simulation problem is to add a private field that holds the pixelToMeter ratio in your class. When you create your bodies you need to divide their width,height with this and when you draw you need to multiply the postions with
this. An example/explanation of this approach can be found at
http://www.progware.org/Blog/post/XNA-for-Windows-Phone-7-and-Physics.aspx